I. Field of the Invention
This invention relates generally to silicon-free metal alloy powder mixtures useful for filling holes and slots and repairing and reforming damaged surface areas in high temperature engine components. In particular, the invention relates to novel metal alloy mixtures which have the ability to repair many service damaged components which are presently considered non-repairable. Also, the present metal alloy powder mixtures can be used in new part fabrication and/or for the reformation of eroded or damaged surface areas, such as the tips of unshrouded blades. The present alloy powder mixtures are used in a novel method for filling large holes, slots and widegap joints, or reforming extended surface areas, which method yields metal deposits with remelt temperatures (i.e., solidus temperatures) substantially greater than those produced by previous filling or repairing or brazing techniques.
II. Description of the Prior Art
It has become increasingly important, especially in high temperature aircraft applications such as, for example, in turbine engine components, to use materials for structural applications that are capable of withstanding the combination of both high temperatures and corrosive attaches normally associated therewith. Stainless steels and the so-called superalloys, such as nickel-base superalloy, have been employed where possible to meet requirements of high strength to weight ratios, corrosion resistance, etc. at elevated temperatures. However, the greatest impediment to the efficient use of these materials has been the difficulty in repairing of service damaged components.
Generally speaking, known brazing filler metal materials do not have the desired properties that are necessary for use in filling relatively large holes, slots and widegap joints and various other types of defects in high temperature superalloys such as those used in turbine engine high temperature components. In addition, known alloy powders and mixtures are completely unsatisfactory for rebuilding or reforming surface areas of high temperature superalloy bodies, such as blade tips, and therefore they are not intended for such use. As a result, superalloy bodies such as engines which develop these types of defects lose efficiency, and parts, many of which are very expensive, must be scrapped. In addition to these problems and disadvantages, conventional brazing filler metals do not simultaneously give good wetting, very limited flow, and the ability to bridge defects so that the defects are repaired without filler material flowing into internal passages in the components. This is as expected because brazing filler metals are designed to flow into spaces via capillary action, i.e., they liquify at the processing or use temperature and are drawn into the joint interfaces being united. Furthermore, known brazing filler compositions do not have the above desired properties along with the ability to provide both excellent high temperature and corrosion resistance and, when properly coated, survive in the harsh environment of a turbine engine. Thus, there is a great need for proper metal alloy mixtures that can be used to repair and/or rebuild surface areas of high temperature superalloy bodies and for techniques of using these mixtures for these purposes.
Previously, repair of high temperature superalloys has been attempted with brazing filler metal compositions but these materials, some of which are disclosed in U.S. Pat. Nos. 4,381,944, 4,379,121, 4,394,347, 4,442,968, 4,444,353, and 4,478,638 have been found ineffective for the reasons stated above.
Smith, Jr. et al U.S. Pat. Nos. 4,381,944 and 4,478,638 relate to alloy powder mixtures formulated to melt and flow into small cracks in superalloy bodies under vacuum conditions and at processing temperatures above about 2124.degree. F. and up to about 2250.degree. F. but below the remelt temperature of preexisting brazes. This is similar to conventional brazing or soldering, requires the use of high processing temperatures which can damage the superalloy body and/or superalloy coatings thereon, and does not permit the alloy powder composition to retain its shape and location on the superalloy body during processing so that surface reformation, such as blade tip reformation, can be made and large cracks can be filled and bridged without run-off or run-in.